Misc #16671

BASERUBY version policy

Ruby 2.7 (MRI) requires Ruby 2.2 or later (== BASERUBY) to build from repository.
Tarball does not need any installed Ruby.
To build latest Ruby from repository, you need to build Ruby 2.2 and later from a tarball.

To use ISeq#to_a (specific format) Ruby 2.2 or later is needed from Ruby 2.7.
The oldest version used by RubyCI machines was Ruby 2.2, so I determined update.
I needed to file a ticket about this version bump, sorry.

Through the discussion around CI, I reached a conclusion "Runtime environment and development environment are different".

Though CentOS and macOS bundles very old ruby, but it's no problem because they are just runtime environment.
If people want to develop Ruby master on those environment, they can install latest stable ruby with tarball.

Therefore BASERUBY can be a reasonable newer stable version.
It means newer than Ruby installed by default on for example CentOS.

I'm not against this issue but for record: commit 8a72c77c7920d129818b7b83bb4fa669cd7e3f7d says "as requested by devs, support for BASERUBY prior to 2.1". and the "devs" here included ko1. At that time his machine was a Panasonic laptop running Windows, and had older BASERUBY. Windows situation got improved since then (we now have CI). This might no longer be a problem.